1. Field of the Invention
The present invention generally relates to a method of detecting life of an image bearing member used in an image forming apparatus for forming an electrostatic latent image in an image bearing member by, for example, an electrophotographic system or an electrostatic recording system and visualizing the electrostatic latent image with a developer, to an image forming apparatus using the above method, and further, to a cartridge detachably attachable to the image forming apparatus.
Here, the image forming apparatus with the electrophotographic system include, for example, an electrophotographic copier, an electrophotographic printer (for example, an LED printer and a laser beam printer), and an electrophotographic facsimile.
The cartridge detachably attachable to the main body of the electrophotograph image forming apparatus indicates the cartridge having at least one of an electrophotographic photosensitive member, charging means for charging the electrophotograh photosensitive member, developing means for supplying a developer to the electrophotographic photosensitive member and cleaning means for cleaning the electrophotographic photosensitive member. In particular, a process cartridge indicates the cartridge in which at least one of the charging means, the developing means and the cleaning means, and the electrophotographic photosensitive member are integrally made into the cartridge, and the cartridge is made detachably attachable to the main body of the electrophotograph image forming apparatus, or the cartridge in which at least the developing means and the electrophotographic photosensitive member are integrally made into the cartridge and the cartridge is detachably attachable to the main body of the electrophotograph image forming apparatus.
2. Related Background Art
Conventionally, in an image forming apparatus of an electrophotographic system such as an electrophotographic copier or a laser beam printer, an electrophotographic photosensitive member as an image bearing member is uniformly electrified by using charging means, and thereafter, the surface is irradiated with light corresponding to image information to form a latent image. Then, a developer is supplied to the latent image using developing means to visualize the latent image, and after the visualized image is transferred to a recording medium, the image is fixed in a fixing apparatus to obtain an image on the recording medium. Further, the electrophotographic photosensitive member after the transfer is cleaned with cleaning means.
In such an image forming apparatus, in order to attain simpleness and easiness of exchange and maintenance of expendable supplies such as the electrophotographic photosensitive member and the developer, there is a process cartridge system in which an electrophotographic photosensitive member, developing means as process means acting on the electrophotographic photosensitive member, charging means, cleaning means, and further, a container for a developer and a container for a waste developer are integrally made into a process cartridge, and the cartridge is detachably attachable to the main body of the image forming apparatus.
According to the cartridge system, a user can conduct maintenance of the apparatus without a serviceman. Images can be formed again by exchanging a cartridge by the user when the developer has run out or when the photosensitive member drum has expired, for example. As described above, the cartridge system can remarkably improve operability of the apparatus, and thus, is widely used in the electrophotograph image forming apparatuses.
In the image forming apparatus of the cartridge system, for example, it is necessary that the user can exchange the cartridge at an appropriate time by notifying the user that the expendable supplies such as the electrophotographic photosensitive member and the developer have expired or that they are approaching the expiry of life.
Conventionally, as a method of detecting life of an electrophotographic photosensitive member having, for example, a cylindrical shape, that is, a photosensitive member drum:
(1) there is a method of detecting life of a photosensitive member drum by integrating the number of sheets of image formation. In the simplest method, in the case where the size of the sheets of the recording medium, on which an image is formed, differs, for example, between A4 size and A3 size, the sheets of the recording medium are counted as the same. However, in this method, the precision of detecting the life of the photosensitive member drum is not satisfactory. Further, with only integration of the number of sheets of image formation, rotation time of the photosensitive member drum per one sheet of the recording medium differs depending on how many sheets are conducted with image formation per one job, that is, how many sheets of the recording medium are conducted with continuous image formation from the start of the image forming operation. Thus, the life of the photosensitive member drum varies in accordance with the rotation time, which is described later. Therefore, in this method, the precision of detecting the life of the photosensitive member drum is not satisfactory.
Moreover, (2) as described in Japanese Patent Application Laid-open No. 4-51259 as a prior art, there is a method of detecting a charge amount of a photosensitive drum with a surface potential sensor. In accordance with this method, in actuality, a reduction of charge potential of the photosensitive member drum or a reduction of latent image contrast can be directly detected with the surface potential sensor. Thus, in comparison with the method of (1) described above, life detection with satisfactory precision is possible, which reflects the state of an output image. However, in order to implement the above method, the surface potential sensor, an electric circuit for processing the output, and the like are needed, and thus, the cost increases. Further, with respect to a longitudinal direction of the photosensitive member drum, only the information on the photosensitive member drum corresponding to the sensor position is data to make a decision. Thus, the detection ability to a partial defect is weak, and there are variation of the surface potential sensor and instability of change with time and the like. Therefore, this method is not necessarily a method of constantly detecting the life of the photosensitive member drum with accuracy.
Furthermore, (3) as a method of improving detection accuracy of the life of the photosensitive member drum while solving the problem of the above method (1), there is disclosed, in Japanese Patent Application Laid-open No. 5-188674, a method of integrating the rpm of the photosensitive member drum instead of integrating the number of sheets of image formation. Based on the same principle, there is a method of integrating the rotation time of the photosensitive member drum. In any of the methods, since, with respect to one image formation, as the size of the recording medium becomes larger, the rpm (rotation time) increases while as the size of the recording medium becomes smaller, the rpm (rotation time) decreases, in accordance with the size of the recording medium, the detection error of the life of the photosensitive member drum due to the size difference of the recording medium becomes smaller in comparison with the case of integrating the number of sheets of image formation. Further, the rpm (rotation time) of the photosensitive member drum is directly integrated irrespective of the number of sheets of image formation per one job, and thus, the precision of the life detection is relatively satisfactory.
As a method which is developed on the basis of the above method (3), there is disclosed, in Japanese Patent Application Laid-open No. 4-98265, a method in which the rpm of the photosensitive member drum at the time of actual image formation is integrated by integrating the rpm of the photosensitive member drum only at the time when a transfer charger as transferring means operates so that the life detection of the photosensitive member drum with more accuracy is possible. Further, there is disclosed, in Japanese Patent Application Laid-open No. 6-180518, a method in which the rpm of the photosensitive member drum during an electrification process of the photosensitive member drum, and the rpm of the photosensitive member drum while a cleaning member that cleans the photosensitive member drum contacts, are respectively integrated, and the expiry of life of the photosensitive member drum is determined on the basis of comparison of the respective rpms and the setting values (life).
Further, the following method is known as a method of notifying a user of timing for a process cartridge exchange. Namely, in a method disclosed in Japanese Patent Application Laid-open No. 5-333626, timing for the process cartridge structured with a cleaner (cleaning means) and an electrophotographic photosensitive member is firstly notified to the user on the basis of the life of the electrophotographic photosensitive member. That is, the apparatus is stopped at the time when the electrophotographic photosensitive member reaches the life of a guarantee by integrating the number of sheets of image formation and becomes unusable. Besides, as exchange display operation based on the life of the electrophotograph photosensitive body, the apparatus urges a user to prepare a cartridge for exchange by displaying that the exchange time is approaching the life of a guarantee, or in a case where the cartridge is continuously used, the apparatus warns that the time to stop the apparatus is approaching. Further, in accordance with this conventional technique, the apparatus is structured such that the timing for a cartridge exchange can be notified to the user also based on a toner capacity of a recovered toner containing portion of the cleaner. That is, an on-time of a driving motor for toner replenishment is integrated, and the apparatus is stopped in accordance with the integration time which is expected to come the earliest under the worst condition in which various variations are considered. Also in this case, as the exchange display operation based on the capacity in the toner containing portion, the display to prompt the user to exchange a cartridge at the time when the integration time of the on-time of the driving motor for toner replenishment becomes a certain value is made, and the display to notify the user that the time to stop the apparatus is approaching is made at a later integration time.
In this conventional technique, the operation based on the life of the electrophotographic photosensitive member and the operation based on the toner capacity in the recovered toner containing portion of the cleaner are generally set so as to have priority over the number of prints, that is, the life of the electrophotographic photosensitive member. However, when toner replenishment is frequently conducted because of unusual high image density, and the recovered toner container is about to be filled earlier compared with the life of a guarantee (the number of sheets of a guarantee) of the electrophotographic photosensitive member, an action based on the toner capacity of the recovered toner container works.
Here, in the technique disclosed in Japanese Patent Application Laid-open No. 5-333626, the process cartridge is provided with storage means, the total electrification time of a primary electrifier provided in the image forming apparatus is collectively written in the storage means through a CPU provided in the image forming apparatus at the time of the exchange of the process cartridge, and also, the subsequent electrification time of the primary electrifier Is written and stored in the storage means. Then, the storage means of the spent process cartridge is collected and analyzed, whereby the rpm of the photosensitive member drum at present, and the total amount of discharge time of corotron and the like of the image forming apparatus in which the spent process cartridge has been used can be known with accuracy, and information collection to the image forming apparatus can be conducted at intervals of the exchange of the process cartridge. The above is disclosed. More specifically, the operation cycle number of the photosensitive member drum, the exchange time of an ozone filter, the abrasion (or wear) data prediction of the photosensitive member drum, and the like of the image forming apparatus at the time of the exchange of the process cartridge can be known.
However, the determination of the expiry of life of the photosensitive member drum in the technique disclosed in this application is based on the number of sheets of image formation in the end. As described above, there is no change in the point in that the precision of the life prediction of the photosensitive member drum based on the number of sheets of image formation is not satisfactory.
On the other hand, in recent years, as a developing apparatus for developing a latent image formed on an electrophotographic photosensitive member, there is a apparatus in which so-called one component developer, which substantially contains toner as its only constituent, is used. In this developing apparatus of a one component developing system, mixture of toner and carrier, agitation, and control of toner density (the ratio of the toner to the total amount of the toner and the carrier) are not necessary, dissimilar to a so-called developing apparatus of a two component developing system. Thus, miniaturization of the apparatus and low cost can be realized, and also, exchange work of the developer becomes unnecessary, which is very effective in a printer or the like desired to be maintenance-free. If non-magnetic toner is used as the toner for the one component developer, it becomes unnecessary that a developer carrying member for carrying a developer to an electrophotographic photosensitive member is provided with a magnet roll. Thus, the miniaturization of the apparatus and the low cost can be further realized.
As the developing apparatus of a one component developing system, there is known a so-called developing apparatus of a contact one component developing system comprising: a developer container (hopper) for containing one component developer (toner); a developer carrying member (developing roller) having a roller shape or the like for carrying toner to a latent image on an electrophotographic photosensitive member, which is provided adjacent to the developer container; a toner supply roller rotating in the same direction as the developing roller while contacting the developing roller; and developer layer thickness regulating means (regulating blade) having a blade shape or the like for regulating the toner amount carried on the developing roller, in which the toner in the hopper is carried to the developing roller by the toner supply roller, a toner thin layer is formed on the developing roller by the regulating blade, and the toner thin layer is made in contact with the electrophotographic photosensitive member, to thereby develop the electrostatic latent image formed on the electrophotographic photosensitive member.
In a case where the non-magnetic toner is used as the toner for the one component developer, the regulating blade, which is an elastic blade or the like, is made in contact with the developing roller, Coulomb force due to charge of toner or triboelectrification is utilized to form the toner thin layer on the developing roller, and thus, supplying and carrying toner are conducted.
Further, in recent years, a contact electrifier is widely being used instead of a corona electrifier which has been conventionally widely used as an electrifier for performing an electrification process with an electrophotographic photosensitive member. The contact electrifier has many merits-that lower applied bias is sufficient for the contact electrifier compared with the corona electrifier, that a very small amount of ozone is generated, that the number of the required components that structure the electrifier are small, and that the electrifier is provided at low cost.
Such a contact electrifier is roughly divided into a brush electrifier and a roller electrifier in accordance with a shape of a charging member to be used. The brush electrifier has problems of a track of the brush, a bend of the brush in a case where the electrifier is made in contact with the electrophotographic photosensitive member for a long period of time, and the like. On the other hand, the roller electrifier has difficult problems in that resistance regulation of the roller is necessary in order to obtain uniform electrification, in that contamination of a drum has to be prevented, which arises from bleed from rubber that constitutes the roller, and in that there is a strict limitation on the shape, surface property and the like of the roller in order to obtain uniform electrification.
As the voltage applied to the contact charging member, only a DC bias (hereafter, referred to as xe2x80x9cDC electrificationxe2x80x9d) and an AC bias superposed on a DC bias (hereafter, referred to as xe2x80x9cAC electrificationxe2x80x9d) are given. Generally, there is a feature that the AC electrification enables uniform electrification compared with the DC electrification.
As the AC electrification, there are electrification in which a charging member having a roller shape (charging roller) is used as a charging member, and a DC voltage is superposed on an AC voltage which is twice or more as large as the voltage at the start of discharge of an applied bias (Japanese Patent Application Laid-open No. 63-149669 and Japanese Patent Application Laid-open No. 1-267667), electrification in which a conductive brush is used as an electrification member, and a DC voltage is superposed on an AC voltage which is twice or less as large as the voltage at the start of discharge of an applied bias (Japanese Patent Application Laid-open No. 6-130732), and the like.
The contact electrification system described above has merits that a small amount of ozone is generated, that the number of the required components that structure the electrifier are small, and that the electrifier is provided at low cost. However, the damage given to the electrophotographic photosensitive member is larger compared with corona electrification. In particular, the tendency is conspicuous in case of using an OPC photosensitive member drum.
Further, even in the same contact electrification method, the damage given to the electrophotographic photosensitive member varies according to the applied voltage to the charging member, and as the applied voltage increases, the damage given to the electrophotographic photosensitive member becomes larger. In case that only the DC voltage is applied as an electrification bias, the damage increases in comparison with the case where the photosensitive member drum is rotated without applying the electrification bias. Moreover, it is found out that the damage (particularly, abrasion amount of the OPC photosensitive member drum) further increases, and the damage is about several times as large as the damage in a case where only the DC voltage is applied as the electrification bias when the AC voltage superposed on the DC voltage is applied as the electrification bias.
In particular, if the AC voltage which is twice or more as large as the voltage at the start of discharge is applied, the increase phenomenon of the damage to the electrophotographic photosensitive member becomes conspicuous. However, even if the AC voltage which is twice or less as large as the voltage at the start of discharge is applied, the damage is about several times as large as the damage in a case where only the DC voltage is applied.
Further, also in a case where the frequency of the AC voltage applied as the electrification bias is made larger, there is a tendency that the damage to the electrophotographic photosensitive member (in particular, the OPC photosensitive member drum) increases.
On the other hand, as described above, in recent years, there is a method in which a developing roller as a developer carrying member is made to carry one component developer, and the developing roller is made in contact with a photosensitive member drum to develop an electrostatic latent image on the photosensitive member drum, but the photosensitive member drum is scraped by contact rotation of the developing roller as well.
In general, in a case where a one component non-magnetic developing apparatus is used, in which a developing roller contacts a photosensitive member drum, a peripheral speed of the developing roller is increased with respect to, for example, a peripheral speed of the photosensitive member drum in order to secure the required density. Particularly, in a case where the developing roller has a relative peripheral speed ratio with respect to the photosensitive member drum, there is a tendency that the damage given to the photosensitive member drum increases.
However, in a color image forming apparatus in which an electrostatic latent image on a photosensitive member drum is developed by switching developing apparatuses of a plurality of colors, and in an image forming apparatus in which a spacing mechanism is provided for having a clearance between a developing roller and a photosensitive member drum, and a method of having a clearance between the developing apparatus and the photosensitive member drum at the rotation of the photosensitive member drum during a non-image formation period is adopted in order to prevent fog of contact development, the rotation time of the photosensitive member drum is not proportional to the contact time of the photosensitive member drum and the developing roller.
As apparent from the above description, in the image forming apparatus which is provided with the charging means that electrifies the photosensitive member drum with, for example, contact electrification under a plurality of electrification conditions during image formation and in which both the AC voltage and the DC voltage are used, the damage that the photosensitive member drum receives varies according to the electrification condition. Thus, with the conventional method of detecting life of the photosensitive member drum on the basis of only the rpm of the photosensitive member drum, it is difficult to predict the life of the photosensitive member drum with accuracy.
Further, in a case where the developing apparatus which can be alienated from the photosensitive member drum is used, the rotation time of the photosensitive member drum is not proportional to the contact time of the photosensitive member drum and the developing roller as described above. Thus, in the conventional method of detecting life of the photosensitive member drum on the basis of only the rpm of the photosensitive member drum, it is impossible to predict the life of the photosensitive member drum with accuracy.
Due to the above reasons, there is a fear that inconvenience occurs such that a warning for a cartridge exchange is not issued although the photosensitive member drum has expired to generate an image defect or such that the warning for a cartridge exchange is issued although the photosensitive member drum has not actually expired yet.
Accordingly, a main object of the present invention is to provide a method of detecting life of an image bearing member in which that the image bearing member has reached the expiry of life or is approaching the expiry of life can be detected with accuracy, an image forming apparatus, and further, a cartridge detachably attachable to the image forming apparatus.
Another object of the present invention is to provide a method of detecting life of an image bearing member in which an exchange time based on the life of the image bearing member and or that the exchange time is approaching can be accurately notified, an image forming apparatus, and further, a cartridge detachably attachable to the image forming apparatus.
Still another object of the present invention is, particularly, to provide a method of detecting life of an image bearing member in which that the image bearing member has reached the expiry of life or is approaching the expiry of life can be detected with accuracy in a case where the image bearing member is electrified under a plurality of electrification conditions and developing means can be alienated from the image bearing member, an image forming apparatus using the method, and further, a cartridge detachably attachable to the image forming apparatus.